#include <bits/stdc++.h>

using namespace std;

struct ListNode
{
    int val;
    ListNode *next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode *next) : val(x), next(next) {}
};


class Solution {
public:
    ListNode* middleNode(ListNode* head) 
    {
        ListNode *slow = head, *fast = head;
        while (fast && fast->next)
        {
            slow = slow->next;
            fast = fast->next->next;
        }
        return slow;
    }
};